The objective of the proposed research is to develop active-site directed reagents which are irreversible inhibitors of acyl-CoA utilizing enzymes. The reagents which we synthesize and test are all analogs of CoASH. Highly reactive functional groups, each of which has been shown to react with amino acid side chains by other workers, are incorporated into CoASH, usually at the thiol end of the molecule. Photo-activated functional groups of the aryl-azide type are also attached to CoASH. We intend to exploit the active-site-directed reagents for probing the structure and catalytic mechanisms of certain acyl-CoA utilizing enzymes. Enzymes to be investigated this year are fatty acid synthetase from lactating rat mammary gland, short-chain acyl-CoA hydrolase from beef kidney, and long chain acyltransferases (membrane-bound) from liver.